A single-stranded DNA-binding protein promotes the binding of the purified oestrogen receptor to its responsive element.

The purified human oestrogen receptor (hER) does not form a detectable complex with an oestrogen responsive element (ERE) under conditions where hER-ERE complexes are readily formed with crude extracts from Hela or yeast cells expressing the hER. This indicates that other factor(s) are necessary for ER-ERE binding. Such a ER DNA binding stimulatory factor (DBSF) has been purified from the yeast Saccharomyces cerevisiae. It is a 45 kDa single-stranded DNA-binding protein (SSB) which cannot be substituted for by the purified E. coli SSB.